Mortgage Acceleration Calculator — Pay Off Early & Save Interest
Enter your loan details and a monthly extra payment to discover how many years you can shave off your mortgage and how much total interest you will save.
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years
Total interest saved over the life of the loan by making extra payments
How does this calculator work?
Extra monthly principal payments reduce the balance faster, cutting the interest charged every subsequent month. The compounding benefit means even a modest extra payment saves thousands over the loan life. Standard payment = P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1); the accelerated payoff is then simulated month-by-month until the balance reaches zero.
Formula
How this is calculated
Every mortgage payment first covers that month's interest charge — balance × monthly-rate — and the remainder reduces the principal. With a standard schedule, the extra principal reduction per payment is fixed, so the balance declines slowly at first and faster later. Adding an extra amount each month accelerates this decline because each extra dollar paid reduces the balance that future interest is charged on, compounding the savings over time.
The calculator first computes the standard fixed monthly payment using the amortization formula P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1), where r is the monthly interest rate and n is the total number of payments. It then simulates the accelerated payoff month by month: each month the interest charge is computed on the remaining balance, the accelerated payment (regular + extra) is applied, and the process repeats until the balance reaches zero. The month at which the balance is cleared defines the new payoff date.
Total interest for each scenario is the sum of all monthly interest charges across the simulation. The difference is the interest saved. The chart shows both balance trajectories — the wider gap between the two curves, the greater the acceleration effect. Results assume a fixed interest rate and equal payments; variable-rate mortgages or lump-sum prepayments require separate analysis.
Frequently asked questions
Yes. Because every extra dollar reduces the balance that interest accrues on for every remaining month, even a modest extra payment produces compounding savings. An extra $50/month on a 30-year $300,000 mortgage at 6.5% saves over $30,000 in interest and cuts the term by more than two years.
When specifically designated as "extra principal payment," yes — the full extra amount reduces the balance. If you simply pay more than the required amount without specifying, some lenders may apply the overpayment to the next scheduled payment. Check with your lender.
A biweekly payment plan has you pay half your monthly payment every two weeks, resulting in 26 half-payments — effectively 13 full payments — per year instead of 12. That one extra payment per year achieves a similar (though smaller) acceleration effect. This calculator lets you model any extra monthly amount, including the equivalent of one extra payment spread over twelve months.
Also known as
TG we-Calculate Editorial Team. (2026). Mortgage Acceleration Calculator — Pay Off Early & Save Interest [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/mortgage-acceleration-calculator
TG we-Calculate Editorial Team. "Mortgage Acceleration Calculator — Pay Off Early & Save Interest." TG we-Calculate. 2026. https://we-calculate.com/calculator/mortgage-acceleration-calculator.
TG we-Calculate Editorial Team, "Mortgage Acceleration Calculator — Pay Off Early & Save Interest," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/mortgage-acceleration-calculator
@misc{wecalculate_mortgage_acceleration_calculator, title = {Mortgage Acceleration Calculator — Pay Off Early & Save Interest}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/mortgage-acceleration-calculator}}, year = {2026}, note = {TG we-Calculate} }
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